1.Field of the invention
The present invention relates to an electronic cooling device using temperature reduction caused by the Peltier effect and, more particularly, to a multi-stage electronic cooling device wherein Peltier-effect thermoelectric elements are arranged on a plurality of stages.
2.Description of the Related Art
A multi-stage electronic cooling device having a two or more-stage construction as shown in FIG. 9 is disclosed in Japanese patent application laid-open No. Hei 2-10781. The cooling device has six stages, on each of which thermoelectric couples A, each formed of an n-type semiconductor 21 and a p-type semiconductor 22, are disposed so that n-type semiconductors 21 and p-type semiconductors 22 are alternately arranged. The thermoelectric couples A are connected in series by electrodes formed on base plates 23. When a current is passed through the thermoelectric couples A on each stage, an upper-side base plate portion gives off heat and is cooled, so that the uppermost base plate 23a is cooled to a low temperature.
In the conventional multi-stage electronic cooling device, there is a need to electrically connect the electrodes on different stages. Although a method of connecting the electrodes on different stages is not specifically described in any literature known to the present inventors, methods as illustrated in FIGS. 10 and 11 can be considered. In the method shown in FIG. 10, end electrodes of different stages are connected by lead wires that are soldered to the electrodes. In the method shown in FIG. 11, end electrodes of difference stages are connected by plates of copper, which is a good electrical conductor. The copper plates are soldered to the electrodes.
However, if the method shown in FIG. 10 is employed, the lead wires considerably protrude from sides of the electronic cooling device, resulting in an increased total size. This drawback is significant since the electronic cooling device is normally required to have a compact body. If the method shown in FIG. 11 is employed, cracks are likely to occur in bent portions of the copper plates. Such cracks impede stable current through the electronic cooling device, causing a reduction in product reliability. Furthermore, in either of the methods shown in FIGS. 10 and 11, if the chip height of the thermoelectric semiconductors is reduced, the clearance between the base plates and the connecting parts, such as lead wires, copper plates or the like, becomes very small, making it very difficult or impossible to solder the connecting parts. If soldering is possible, the soldering operation will be complicated.